The germguardian True HEPA Replacement Filter C PET is a combination filter that incorporates multiple layers of filtration including: a pre-filter, charcoal filter and True HEPA filter, to help improve indoor air quality. The Pet Pure treatment includes an anti-microbial agent to inhibit the growth of mold, mildew and odor-causing bacteria on the surface of the filter. For use with germguardian 3-in-1 Air Cleaning Systems ? 5000 model series. It is recommended that the filter be replaced every 6-8 months depending on use.